This invention relates to a sintered rotor for a rotary pump and a manufacturing method for the rotor.
An inner rotor for a rotary pump utilizing the trochoidal curve, when given a diameter A of a base circle, a diameter B of a rolling circle, an eccentricity e, and a diameter C of a locus circle (tracking circle), can obtain an inner rotor curve TC as the envelope of a circular-arc group centered on the trochoidal curve T, and also a theoretical curve of an outer rotor is obtained.
In this case, a combinational gap g between the inner and outer rotors from the above dimensions, that is the gap formed on the opposite side from where the inner and outer rotors touch, is zero so that both the rotors are not rotatable. Hence, in fact, the curve of the inner rotor is corrected to be smaller, or that of the outer rotor is corrected to be larger, thereby producing the combinational gap g through which the rotors become rotatable.
The gap g as a function of the rotational position (rotary angle) of the inner rotor relative to the outer rotor before and after the correction is shown respectively by the dotted and solid curves in FIG. 2.
Such correction for the curves at present is carried out experimentally so that the combinational gap g of each part in a commercial rotary pump utilizing the trochoidal curve is not constant but rather fluctuates with changes in rotary angle .theta., in which the regulation S is given by the equation: ##EQU1## where g max and g min are respectively the maximum value and minimum value of the combinational gap g over a complete revolution of the inner rotor within the outer rotor. The regulation S of the rotors which have the combinational gap g prior to correction as shown by the dotted line in FIG. 2, is about 60.about.80%, which is made smaller by the correction shown by the solid line in FIG. 2. In other words, the combinational gap at each part is made about constant and smaller by the correction, thereby enabling an improvement in the performance of the pump.
However, when the maximum combinational gap g max. is made smaller, the minimum combinational gap g min. portion causes interference with teeth which leads to poor rotation of the pump, whereby the combinational gap is restricted in its diminution.
For diminishing the gap regulation the following methods are proposed:
(a) To select a smaller eccentricity ratio f.sub.e =(e/B) for the inner rotor.
(b) To properly correct the theoretical curve of the outer rotor.
(c) To reasonably combine the above methods (a) and (b).
In addition, if the correction by the method (b) is made properly, even if the eccentricity ratio of the inner rotor is not reduced in accordance with the method (a), the regulation S can be made smaller to a certain, but limited, extent.
Conversely, even if the eccentricity ratio of the inner core is reduced in accordance with the method (a), the correction of the curve of outer rotor, if not proper, cannot diminish the regulation S.
This inventor has filed a Japanese Patent Application (disclosure No. 148992 (1980)) for the rotor of a rotary pump of the curve formed by combining the methods (a) and (b) to have a regulation S of 60% or less and has also filed a Japanese Patent Application (application disclosure No. 148991 (1980)) directed to the correction for the theoretical curve of the outer rotor.
The inventor, after conducting research since then, has found out that, in the case where the number of teeth of the inner rotor in the Japanese Patent Application disclosure No. 148992 (1980) is the integer n, not only the eccentricity ratio f.sub.e but also a ratio A/B between the base circle diameter A and the rolling circle diameter B are determined according to the integer n, whereby the method of correcting the curve can correspond not only to the number of teeth of the integers n=1, 2, 3 . . . , but also to the special tooth form wherein the number of teeth includes those represented in the hatched area in FIG. 3, in which n=4.5, n=5.5 . . . are shown. Furthermore, the inventor has found out that, when this method is applied to the design of a metallic mold used for manufacturing the sintered rotor so that the metallic mold is used to produce the sintered rotor, a desired sintered rotor can be produced. As a result, the inventor has designed this invention.